Caption: Phase contrast cinemicrography of swimming human spermatozoa. Each sperm (spermatozoan) has a rounded head (5 micrometres by 3 micrometres) and a long tail (50 micrometres long), which it uses to both swim and burrow into the egg. The tail propels the sperm cell at about 1 to 3 millimetres per minute by whipping in an elliptical cone. Fertilisation occurs when a sperm's genetic material (deoxyribonucleic acid, DNA) fuses with an egg's DNA, forming a zygote.